Natural killer cells undergo dramatic age-related changes affecting their ability to clear senescent cells, regulate inflammation, and maintain immune surveillance. These immune effectors lose critical functions including receptor balance, metabolic programming, and elimination capacity for damaged cells—a process termed NK immunosenescence. The deterioration directly contributes to increased cancer risk, infection susceptibility, and metabolic dysfunction in aging adults. This positions NK cells as both sentinels of biological aging and potential therapeutic targets for longevity interventions. The emerging field of longevity medicine now views NK cell function as a measurable biomarker of immune aging, though validation for prognostic accuracy remains incomplete. Interventions ranging from lifestyle modifications to cytokine therapies show promise for preserving NK competence. However, most advanced NK-targeted approaches remain experimental outside cancer treatment. The significance lies in reframing aging as partly driven by immune surveillance failure rather than inevitable cellular decline. This systems-level understanding suggests that maintaining robust NK cell function could extend healthspan by preserving the body's natural ability to eliminate damaged cells and regulate tissue homeostasis—making NK cells actionable targets for precision longevity medicine.